Preparing an Expert Witness for Trial

Almost every witness who is called at a trial is there to testify because they have participated in, heard or witnessed something relevant to the issues in the action.  However, there is a category of witness who can testify beyond what they have observed or experienced.  These witnesses are expert witnesses.  Expert witnesses are permitted to testify about their opinions and not just their personal knowledge.  Often these opinions are based on hearsay evidence or assumed facts. Therefore the weight that the jury or judge gives to expert testimony is directly related to the qualities or credentials that the expert has to offer.  It is important that you select the right expert in each case and that you prepare that expert meticulously before trial. It is only by thorough preparation of the expert witness that you can be sure that your client will receive the benefit of persuasive expert evidence at trial.

Steps to take prior to retaining the expert

Prior to retaining the expert you should do a thorough and close review of the expert’s curriculum vitae (“C.V.”).  It is important to review the C.V. for things that are inaccurate or irrelevant to the issue that the witness will be testifying about.  Frequently experts’ C.V.’s are not written with testifying in court in mind.  It can be devastating to an expert’s credibility if it is brought to light in cross-examination that their C.V. contains exaggerations or half-truths.

You should also always examine the C.V. in an attempt to weed out anything that may suggest bias on the part of the witness or that they are a professional witness who only does work for plaintiffs. For example, if the C.V. contains numerous references to the expert having been retained by plaintiffs’ firms those are best removed.

It can also be devastating to your case if defence counsel proves on cross-examination that your expert is not a true expert in the field that they are testifying about. For example, our firm was involved in a case in which a labour economist was called by the defence to rebut the evidence of a health care economist on the issue of inflation as it relates to future health care costs. It was relatively simple to marginalize the opinion of the labour economist on this issue simply because he did not have special expertise in the field of health care economics.

When selecting an expert you should always look at the C.V. as if you are the judge or jury hearing the case. Which credentials would you consider important? For example, in a medical malpractice case would you rather have a standard of care doctor who practices medicine in a large Toronto teaching hospital or a doctor who practices in the same type of tertiary hospital where the negligence took place?

It is also important to assess how the witness will do if they have to testify in court.  It is not helpful to have a witness who has an excellent resume but who is a terrible witness at trial.  You may want to speak to the proposed expert about their experience testifying in court. It is also helpful just to chat with an expert to get a sense of what type of person they are and how they will come across to a judge or a jury.

The Expert’s Report

In order to have an expert testify at trial his or her findings, opinions, and conclusions must have been recorded in an expert report which was served on the opposing party.  The Rules of Civil Procedure were amended on January 1, 2010 to revise the timeline and contents requirements for expert reports.  Rule 53.03 says that an expert report must be served at least 90 days before the Pre-Trial Conference.  A responding report must be served at least 60 days before the Pre-Trial Conference. Supplementary reports can still be served 30 days prior to trial.

The newly created Rule 53.03(2.1) provides the necessary information that must be contained within the report.  This includes:

1.      The expert’s name, address and area of expertise.

2.      The expert’s qualifications and employment and educational experiences in his or her area of expertise.

3.      The instructions provided to the expert in relation to the proceeding.

4.      The nature of the opinion being sought and each issue in the proceeding to which the opinion relates.

5.      The expert’s opinion respecting each issue and, where there is a range of opinions given, a summary of the range and the reasons for the expert’s own opinion within that range.

6.      The expert’s reasons for his or her opinion, including,

i. a description of the factual assumptions on which the opinion is based,

ii. a description of any research conducted by the expert that led him or her to form the opinion, and

iii. a list of every document, if any, relied on by the expert in forming the opinion.

7.      An acknowledgement of expert’s duty (Form 53) signed by the expert. O. Reg. 438/08, s. 48.

Meeting with your expert before trial

When meeting your expert witness to prepare for trial it is important to go through a practice run of your proposed examination-in-chief regarding the expert’s qualifications.  This is particularly important if the expert has never given evidence at trial before. It will allow the expert to become used to your style and it will allow you to get a feel for the way that the expert will answer questions in the courtroom.

After you have prepared the expert for examination-in-chief on their qualifications you can then practice cross-examining the expert on any area of their qualifications which is open to attack.  This will help prepare the expert. It will also allow you to work with your expert so that he or she gives the strongest possible answer to any actual cross-examination on qualifications.

The most fundamental advice should be reinforced about cross-examination, “Tell the truth. Listen to the question and answer only the question you are asked”. However the witness should be reminded that they can expand on an answer with a “Yes, but . . .” or a “No, but . . .” answer. An expert should always be told that his or her role is not to engage in argument or debate in order to advocate for your client. They should make concessions where appropriate and try to answer all questions in a full and fair manner.

The next item that should be addressed at your meeting is to spend time briefing the expert on the facts of the case and your theory of the case.  Things might have changed in the months or years since you first retained the expert.  It is key that the expert understands where their evidence fits in and why it is important.  It is also vital that the expert understands where the weak areas of your case are.  Lastly it is crucial to make the expert aware of all evidence that has developed since the expert’s report was prepared and to ask the expert to review any documents that might assist him or her in giving evidence at trial.

When you review the opinions of the comparable defence experts with your expert you should seek your expert’s input into areas on which you might successfully cross-examine the opposing expert.

One matter that is often overlooked is to ensure that the witness understands the legal tests and terminology involved in the case so that they do not accidentally give evidence that harms your case.  For example, it is essential that the witness understand the difference between possibilities and probabilities and that you explain the civil standard of proof.  I always explain that most matters in a civil trial have to proven on a balance of probabilities (i.e. 50.001% or greater) but that the legal test with respect to future losses is that there must be a substantial possibility that the loss will occur[i].  There have been numerous cases in which the plaintiffs have gone down to defeat on the basis of an expert witness saying that there was a chance that something could occur but that this chance does not rise to the level of more likely than not. It is important to work with the expert in advance of trial and prepare carefully worded questions that will bring out their evidence in a way that will increase the chances of weight being given to that opinion.

It is also helpful to work with your expert before trial to come up with a manner in which their opinion can be explained in a logical way using plain language. If possible, you should try to have the expert use demonstrative evidence in order to help the jury or judge understand what is usually complex evidence.


The importance of expert evidence in personal injury cases cannot be overstated.  Preparing for trial is a busy time. It is imperative not to overlook scheduling a meeting with your expert witness in order to prepare him or her for trial.  It is only with a fully informed and prepared expert that a lawyer can be confident that they will be presenting that expert’s evidence in a persuasive and effective manner at trial.

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